The ability to simultaneously transmit both low-frequency and high-frequency signals with significant attenuation between the low-frequency and high-frequency regions is often desired in communications--for example, in frequency-division multiplex systems and in subcarrier multiplex systems. Such an effect can be achieved either through a notch filter, or through a cascade of a low-pass filter and a high-pass filter. Known such filters are active electronic components--that is, they require an external source of power--that tend to be rather complex in structure and expensive, and that tend to take up a significant surface area of a printed-circuit board.